Tuning systems for radio and television receivers typically include a tunable RF stage for selecting the RF signal corresponding to a desired station or channel from a plurality of received RF signals, a tunable local oscillator for generating a local oscillator signal having a frequency corresponding to the desired station or channel and a mixer for heterodyning the selected RF signal with the local oscillator signal to produce an IF signal corresponding to the RF signal.
For some applications such as tuning both VHF broadcast and cable channels, the local oscillator should be capable of being tuned over a very wide range of frequencies (e.g., in the United States from 101-509 MHz).
While the configuration and type of amplifying device that may be employed in the local oscillator may be advantageous with respect to certain characteristics of the local oscillator such as providing a signal drive level and impedance level compatible with the mixer, the configuration and/or type of amplifying device may tend to restrict the tuning range of the local oscillator.